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This bridge is an excellent example of a nationally rare structure type, the concrete curved chord through girder, often called concrete camelback bridges. Michigan was the leader in construction of this bridge type, and Ohio likely would be ranked in second place, although there would not be much competition since it is not apparent that any other states built this structure type in any large quantity. For example, one county in Indiana built concrete camelback bridges, but just the one county. A few states have just one or two examples in the entire state. The remaining states appear to have no examples.
This particular bridge is noted for its good overall concrete condition, as well as for having one of the largest span lengths among surviving examples of this bridge type in Ohio. 60 feet appears to have been the longest concrete girder that most states, including Ohio, felt was economical to construct. Longer spans required a different structure type, or a multi-span design. Only Michigan built larger concrete curved chord through girders, indeed considerably larger, at up to 90 foot spans. However, in the context of Ohio and all states but Michigan, this Ohio bridge is an extremely long example of the bridge type.
HistoricBridges.org strongly disagrees with and disputes the findings of Ohio's historic bridge inventory, which marked all examples of Ohio's concrete curved chord through girders as not eligible for the National Register of Historic Places. The inventory does not recognize that this is a design that only a couple states built in any large quantity. The inventory essentially considers the curved girders as no different than a straight chord through girder, and does not recognize the use of a curve as a technologically significant aspect of the bridges. This finding does not make sense, since when assessing the historic significance of metal truss bridges, Parker, Pennsylvania, and Camelback trusses are given a higher level of significance than Pratt trusses, in recognition of the greater amount of engineering thinking and design, as well as the greater rarity of those truss types. This is no different than a concrete curved chord through girder, which is a rarer bridge type than a straight chord through girder, and has a curve to accomplish the same things as something like a Parker truss: greater strength with less materials. The inventory also comments that the curve is not aesthetic, meaning it is not for decoration, it has a function, but does not consider this fact as contributing to the significance of the bridge type. Their statement is correct, and they should be also noting that it adds to the significance of the bridge. Even though it is structural and serves a utilitarian purpose, the curve is also far more aesthetically pleasing than the appearance of a straight chord through girder. Architectural detailing on the bridges is designed to compliment the shape of the curved girder. Some of the greatest examples of engineering are those which combine function and beauty. This is rarely if ever seen in modern bridges, where any aesthetic elements are usually fake, superficial elements that serve no structural purpose. With a bridge like a curved chord through girder, the bridge structure itself is beautiful. Finally, another odd statement by the historic bridge inventory is that the concrete curved chord through girders were a "dead end" because engineers stopped building them since they could not be economically widened to meet increasing roadway width requirements. Certainly, those bridge types which directly contributed to or led to groundbreaking developments of bridge technology in history should be assigned a high level of significance. HistoricBridges.org does not dispute that. However, to declare a bridge "not historic" because engineers eventually abandoned the structure type does not make any sense. Under this logic, nearly every bridge type except stringer, multi-girder, and various beam type bridges should not be considered historic. The majority of historic bridge structure types are no longer built today because engineers today have reverted to rudimentary concepts like beam bridges out of fear of the fracture critical nature of more sophisticated bridge types like the metal truss bridge. So in a sense, one of the most important types of historic bridges, the metal truss, was a dead end in the development of bridge technology. However nobody attempts to write off metal truss bridges using this logic, and rightly so.
Even if concrete curved chord through girders ended up being a dead end in the development of bridge technology, does that mean that when constructing a history of the development of bridges that the history should be considered complete if concrete curved chord through girders are not mentioned in the history? Only by discussing both the failures and successes of bridge designs can a complete history be conveyed. If the failures are omitted, and incomplete history has been provided. By not listing any of Ohio's curved chord through girder bridges as historic, the inventory is essentially saying that future generations do not deserve to know what a concrete curved chord through girder is. The inventory is saying that future generations deserve to get a skewed, and incomplete interpretation of our past.
The historic bridge inventory would have been far more on target and beneficial to both the public and bridge owners if instead of shooting down an entire bridge type as worthless and beneath notice they had focused on identifying those examples which stand out as noteworthy and designating them as historic. The inventory should have picked out a selection of surviving bridges that were either older examples or longer spanning examples and also had good structural condition and designated them historic. Instead, today, nobody really has a clear picture of Ohio's concrete curved chord through girders, and which ones are most important.
Information and Findings From Ohio's Historic Bridge InventorySetting/Context The bridge carries a 2 lane road over a stream in a sparsely developed, rural setting. Physical Description The 1 span, 62'-long, reinforced-concrete thru girder bridge has paneled, shaped girders with blocky end posts and articulated floorbeams. Summary of Significance The 1928 thru girder bridge is a late and undistinguished example of a standardized bridge type in use from the mid 1910s to 1930s. It is not technologically significant. Reinforced-concrete thru girder bridges are composed of a pair of cast-in-place longitudinal girders and transverse floorbeams or deck slab (the former is the case with most Ohio examples) that are connected by the arrangement of the steel reinforcing bars. The roadway passes between the paired girders, which are the main supporting members and also serve as railings. The girders are commonly very large in appearance (18"" to 30"" wide and 4' to 6' deep) and have deep panels to save on weight. The depth of the girders is related to span length with the longer the span the greater the depth. In many cases, the girders are shaped to achieve the greatest depth of beam at mid-span where it is required to support the design moments (stresses). The shaped girder is a design detail to accommodate longer and/or wider spans and/or heavier design loads, it is not aesthetic. Like other reinforced-concrete bridge types, including the slab and T beam, the thru girder appeared nationally and in Ohio during the first decade of the 20th century. The oldest surviving example in the state, dated to 1905, is located in Morrow County (5930669, Phase 1A Survey, 2008). In Ohio, the type does not appear to have been widely used until after its adoption as a state standard in 1915. Of the approximately 60 identified surviving examples, only three are confirmed to predate 1915. Between 1915 and 1924, the department issued standard plans for thru girder bridges in span lengths ranging from 27' to 65' and roadway widths from 16' to 24', which account for the vast number of Ohio's surviving examples. They also developed an unusual, and perhaps unique to Ohio, cantilevered thru girder design that was adopted as a standard in 1922. The only known surviving example of the cantilevered design is in Gallia County (2742322). The thru girder bridge type played a prominent role in state and county efforts to improve Ohio's roads and bridges in the 1920s, but over time it proved to be one of the least successful of the standard designs and its use was diminishing by 1929 and had ended by 1940. The majority of Ohio's surviving examples (35 of 60) date from 1922 to 1930. Over time, the thru girder proved to be less economical than T beams for the same range of span lengths and was limited to relatively narrow roadway widths (about 24' max.). By 1928, George A. Hool, a noted authority on reinforced-concrete bridge construction, reported that ""from a standpoint of economy, the thru girder should not be built except where insufficient headroom or other local conditions prevent the use of the deck girder [T beam]."" Thru girders were also difficult to widen, a concern that was increasingly on the minds of bridge engineers by the late 1920s. The body of engineering knowledge soon reached the conclusion that thru girders were not as successful or versatile as other standard types. The thru girder can be viewed as a ‘dead end' in the evolution of bridge technology, and this limits the bridge type's significance. Many state highway departments did not use thru girders or stopped building them in the 1920s. And even though Ohio's engineers continued to use thru girders somewhat longer than engineers in many other states, they reached the same conclusions about their disadvantages. The thru girder's contribution to the historical development of Ohio's highways simply was not as great as many other standard types because of its limitations and shorter period of use. Bridge Considered Historic By Survey: No |
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